1. Field of the Invention
The present invention relates to an operation microscope for illuminating and observing eyes to be examined, of a subject such as a patient in diagnosis, medical treatment and operation in ophthalmology.
2. Description of Related Art
An operation microscope is known which illuminates eyes of a subject such as a patient with an illumination optical system and with which an observer can stereoscopically observe the illuminated eyes through a binocular stereoscopic observation optical system in diagnosis, medical treatment and operation in ophthalmology.
However, in the case where an eye is illuminated with a conventional operation microscope, a cornea of the eye to be examined acts as a convex reflective mirror, so that a virtual image of the illumination light source is formed on the focal surface of the cornea. For this reason, as shown in FIG. 1, the virtual image A of the illumination optical source of the illumination optical system is observed in the observation optical system. Thus, it is a disadvantage that the virtual image A of the illumination light source would obstruct the observation when the observer observes the inherent image Ea of the eye to be examined.
Although the virtual image of the illumination light source observed in the observation optical system is not so large in physical size, this virtual image seems as if the light source was present on the cornea. Accordingly, the virtual image is too bright in comparison with other portions, and then it is difficult to observe the other portions by the observer.
Also, blurs or the like caused by diffused reflection produce in the vicinity of the virtual image of the illumination light source. Accordingly, also in this case, the observer observes the vicinity of the virtual image with difficulty.
Further, since the virtual image of the illumination light source is extremely bright, the virtual image offsets the observation light from a portion deeper from the eye to be examined than the portion where the virtual image is positioned, so that it is difficult to observe the deep portion. Also, the attention of the observer would be always dispersed due to the presence of the virtual image, so that the observer cannot concentrate his or her attention to the observation of other portions.
Furthermore, when the virtual image of the illumination light source is incident into the observation optical system, there is a fear that the internal reflection would occur within the observation optical system. If such internal reflection would occur, a flare or a reduction in contrast of the observation image would be caused, resulting in degradation of the condition of the observation image.
On the other hand, according to an operation microscope disclosed in the publication of Japanese Examined Patent Application No. 7-71551, a light absorbing filter is provided in a plane conjugative with an object surface of a central region of the illumination optical path. Therefore, a central shade equal to a pupil diameter is caused in the cornea of the eye to be examined, and then a retina damage of the eye to be examined may be prevented. In an operation microscope with such a structure, the virtual image of the illumination light source as described above is not observed in the observation optical system. However, since the pupil region is not observed at all in such an operation microscope, it is a disadvantage that this operation microscope could not be used for the operation that needs the observation of the pupil region such as crystal lens extracting operation.